1. Field of the Invention
The present invention relates to a spread illuminating apparatus, and more particularly to a spread illuminating apparatus used as an illuminating means for a reflection-type liquid crystal display.
2. Description of the Related Art
A liquid crystal display which is characterized by its small thickness, small occupied volume and light weight is used on many electrical products such as mobile phones and personal computers. Since a liquid crystal, which is a component member of the liquid crystal display, does not emit light by itself, the liquid crystal display requires an illuminating means for illuminating the liquid crystal when used in a place where sufficient sunlight or light from a lighting equipment is not available. Accordingly, it is also desired that the illuminating means be compact in size and low in power consumption. Therefore, it is essential to efficiently use light emitted from the illuminating means. An example of conventional spread illuminating apparatus to answer such demands is shown in FIG. 4.
A spread illuminating apparatus 1xe2x80x2 in FIG. 4 is generally composed of a transparent substrate 2 made of a light-transmissible material and a light source 5 disposed close to an end surface 8 of the transparent substrate 2 and is adapted to make light emitted from the light source 5 enter the transparent substrate 2 thereby to illuminate a liquid crystal display (not shown) provided under the transparent substrate 2.
The light source 5 is composed of a light conductive member 3 made of a transparent member and shaped bar-like, and a spot-like light source (e.g. a light emitting diode) 4 provided at one end of the light conductive member 3. The light conductive member 3 is provided with an optical path conversion means 12. The optical path conversion means 12 is formed such that grooves having, for example, a triangular shape in section are disposed on a surface of the light conductive member 3 opposite to a surface 9 facing the end surface 8 of the transparent substrate 2, whereby light emitted from the spot-like light source 4 is made to enter the end surface 8 of the transparent substrate 2 in a substantially uniform manner. The light conductive member 3 is disposed along the end surface 8 of the transparent substrate 2 at a prescribed distance therefrom with the surface 9 facing the transparent substrate 2.
A frame (a light reflection member) 13 is provided around the light conductive member 3 in order to make the light emitted from the spot-like light source 4 efficiently enter the transparent substrate 2. The frame 13 is formed substantially in a U shape and covers the longitudinal surfaces of the light conductive member 3 except the surface 9 facing the transparent substrate 2. A film having a metal such as silver evaporated on, a hard resin member having a white film or the like adhered to, or a bent metal plate of aluminum or stainless steel is attached to the inner surface of the frame 13.
A light reflection pattern 19 is formed on an upper surface 16 of the transparent substrate 2. The light reflection pattern 19 is composed of grooves 17 triangular in section and flat portions 18 adjacent to the grooves 17. And, the grooves 17 and the flat portions 18 are formed in parallel to the light conductive member 3 at prescribed intervals. The grooves 17 are each formed with a different width so that light which comes from the light conductive member 3 and enters the transparent substrates can be reflected substantially uniformly on the entire surface of the transparent substrate 2 irrespective of the distance from the light conductive member 3 (the light source 5) to desirably illuminate a liquid crystal display 10 provided under the transparent substrate 2. Specifically, the ratio of the width of the grooves 17 to the width of the flat portions 18 increases gradually in proportion to the increase in distance from the light conductive member 3.
As described above, the spread illuminating apparatus 1xe2x80x2 is assembled by putting together the transparent substrate 2, the light source 5 (the light conductive member 3 and the spot-like light source 4), the frame 13, and others. In order to achieve clearer images with the spread illuminating apparatus 1xe2x80x2 thus constructed, it is desirable for light coming from the light conductive member 3 and entering the transparent substrate 2 to be efficiently reflected by the light reflection pattern 19 toward the liquid crystal display. However, actually it is not possible to reflect all incident light toward the liquid crystal display, and part of the incident light undergoes interface reflection (Fresnel reflection) giving a part of reasons for the reduction in contrast. In addition, since the transparent substrate 2 is put together with other members with its surface exposed, it can happen that not only the surface of the transparent substrate 2 is scratched during the assembly process, but also fragments of the transparent substrate 2 or other dusts collect in the grooves 17 of the light reflection pattern 19. These cause a deterioration in the light conduction performance of the transparent substrate 2.
The present invention has been made in view of the above, and an object of the present invention is to prevent dusts from getting on the light reflection pattern of the transparent substrate and also to prevent the surface of the transparent substrate from getting scratched during the process of assembling the spread illuminating apparatus, and another object thereof is to improve the contrast of the spread illuminating apparatus.
In order to solve the above problems, according to a first aspect of the present invention, there is provided a spread illuminating apparatus in which a light reflection pattern is formed on a surface of a transparent substrate made of a light-transmissible material and in which a bar-like light source is disposed close to a side surface of the transparent substrate, wherein a film is disposed on the transparent substrate so as to cover the light reflection pattern. With the film covering the light reflection pattern formed on the transparent substrate, it is possible to prevent the surface of the transparent substrate from getting scratched during the assembly process.
According to a second aspect of the present invention, the film is sealingly fixed to the transparent substrate. Sealingly fixing the film to the transparent substrate surely prevents dusts from getting in between the film and the transparent substrate.
According to a third aspect of the present invention, the film is made of resin, and according to a fourth aspect of the present invention, the film is made of glass. Using resin or glass as a film material enables both an efficient transmission of light and a reduction of interface reflection (Fresnel reflection).
According to a fifth aspect of the present invention, the thickness of the film is 2 mm or less. In consideration of the fact that the amount of light transmitted toward screen observation is reduced due to the film covering the surface of the spread illuminating apparatus, the thickness of the film is set to a prescribed value of 2 mm or less thereby to improve the contrast.